Long chain olefins (C10+) are important starting materials in the production of sulfonate surfactants, in which the olefins are used to alkylate aromatic hydrocarbons and the resultant alkyl aromatics are sulfonated to produce alkylaryl sulfonates. In addition, the alcohols of long chain olefins have considerable commercial importance in a variety of applications, including detergents, soaps, surfactants, and freeze point depressants in lubricating oils. In such applications, the degree and the position of the branching along the carbon chain of the olefin is often critical to the properties of the end product. Thus, for example, highly branched olefins tend to produce surfactants with poor biodegradability, whereas substantially linear olefins tend to produce surfactants with poor hard and cold water cleaning properties. In addition, it is found that lightly branched olefins, where the branching is at the odd-numbered positions in the carbon chain, produce surfactants with enhanced biodegradability as compared to similar olefins where the branching is at the even-numbered positions in the carbon chain.
One potential route for the production of long chain olefins is by the oligomerization of lower (C2 to C6) olefins, typically using an acidic catalyst, such as a zeolite. Thus, for example, it is known from U.S. Pat. Nos. 3,960,978, 4,150,062; 4,211,640; 4,227,992; and 4,547,613 to oligomerize lower olefins over ZSM-5, but the resultant oligomers are essentially linear.
U.S. Pat. No. 5,026,933 describes a process for producing high molecular weight, slightly branched hydrocarbon oligomers from a lower olefin feedstock employing a shape selective crystalline silicate catalyst, ZSM-23, which has been surface deactivated. The resultant oligomer mixture comprises at least 20% by weight of olefins having at least 12 carbon atoms and said olefins having at least 12 carbon atoms have an average of from 0.8 to 2.0 methyl branches per carbon chain. The lower olefin feedstock employed is either propylene or n-butene.
Further investigation of the process described in the '933 patent has now shown that, whereas oligomerization of n-butene produces oligomers in which the majority of the branching appears to be at the odd-numbered positions, such as the 3- and 5-positions, in the carbon chain, oligomerization of propylene produces oligomers in which the majority of the branching appears to be at the even-numbered positions in the carbon chain. Surprisingly, it has also been found that oligomerization of mixtures of n-butene and propylene at molar ratios up to 1:0.49 produces oligomers in which the position of the branching appears to be similar to that obtained with butene alone, i.e., apparently concentrated at the odd-numbered positions in the carbon chain. Since propylene is available in large quantities in a modern integrated oil refinery, this discovery provides an important extension to the applicability of the process of the '933 patent.